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In a Eucalyptus HA configuration there are two Cluster Controllers's (CC) which
are in an active-passive state. One is in "ENABLED" mode and one is "DISABLED" mode.
If a failure occurs, the active CC services moves to the secondary CC system.

If you combine this with Eucalyptus MANAGED or MANAGED-NOVLAN networking
configuration with a private back-end network your Node Controllers (NC) will require a
default gateway for access to external networks and to the Walrus service to download
Eucalyptus Machine Images.